Page 179 - DCAP403_Operating System

Operating System

Notes The hard disk drive as secondary memory is therefore needed for the purpose of installing the
operating system. If there is no operating system then the question arises where to install the
operating system. The operating system obviously cannot be installed in the primary memory
however large that may be. The primary memory is also a volatile memory that cannot be used
for the permanent storage of the system files of the operating system. The operating system

requires the permanent file storage media like the hard disk.
Moreover the hard disk management is an important part of maintaining the computer, since it

requires an efficient management of the data or the user information. The information regarding
the Master Boot Record is stored in the hard disk drive. This is the information that is required
during the start up of the computer. The computer system needs this information for loading the
operating system.

The file management and the resources management is also a part of the hard disk management.

The hard disk management requires an efficient knowledge of the operating system and its
resources and the methods of how these resources can be employed in order to achieve maximum

benefit. The operating system contains the resources and the tools that are used to manage the
files in the operating system. The partitioning and the installation of the operating system itself

may be considered as the hard disk management.
The hard disk management also involves the formatting of the hard disk drive and to check the

integrity of the file system. The data redundancy check can also be carried out for the consistency
of the hard disk drive. The hard disk drive management is also important in the case of the
network where there are many hard disk drives to be managed.
Managing a single hard disk in a single user operating system is quite easy in comparison with
the management of the hard disk drives in a multi user operating system where there is more
than one user. It is not that much easy since the users are also required to be managed.

9.8 Swap Space Management

Swap space is an area on a high-speed storage device (almost always a disk drive), reserved
for use by the virtual memory system for deactivation and paging processes. At least one swap
device (primary swap) must be present on the system.
During system startup, the location (disk block number) and size of each swap device is displayed
in 512-KB blocks. The swapper reserves swap space at process creation time, but do not allocate
swap space from the disk until pages need to go out to disk. Reserving swap at process creation
protects the swapper from running out of swap space. You can add or remove swap as needed
(that is, dynamically) while the system is running, without having to regenerate the kernel.

9.8.1 Pseudo-Swap Space

When the system memory is used for swap space then it is called pseudo-swap space. It allows
users to execute processes in memory without allocating physical swap. Pseudo-swap is
controlled by an operating-system parameter.
Typically, when the system executes a process, swap space is reserved for the entire process, in
case it must be paged out. According to this model, to run one gigabyte of processes, the system
would have to have one gigabyte of configured swap space. Although this protects the system

from running out of swap space, disk space reserved for swap is under-utilized if minimal or no
swapping occurs.
When using pseudo swap for swap, the pages are locked; as the amount of pseudo-swap
increases, the amount of lockable memory decreases. Pseudo-swap space is set to a maximum
of three-quarters of system memory because the system can begin paging once three-quarters of

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